<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
      .box {

width: 500px;

height: 400px;

margin: 40px auto;

background-color: #2b92d4;

border-radius: 50%;

box-shadow: 0 1px 2px rgba(0, 0, 0, .3);

animation: breathe 2700ms ease-in-out infinite alternate;

}

@keyframes breathe {

0% {

  opacity: .2;

  box-shadow: 0 1px 2px rgba(255, 255, 255, 0.1)

 }

50% {

  opacity: .5;

  box-shadow: 0 1px 2px rgba(18, 190, 84, 0.76)

 }

100% {

  opacity: 1;

  box-shadow: 0 1px 30px rgba(59, 255, 255, 1)

 }

}
    </style>
</head>

<body>
<div class="box"></div>
</body>

</html>